The Better to Hear You With

Praying mantises were thought to be deaf until a scientist discovered the insects have a single ear that enables them to pick up sounds far beyond the hearing range of humans

12-01-2009
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Doreen Cubie

PRAYING MANTISES often mimic a leaf or a twig, and according to University of Maryland neuroscientist David Yager, they also can do an excellent imitation of a fighter jet. When a flying mantis is trying to escape from a bat, one of its primary nocturnal predators, it can suddenly pull up in midair, turn to the side and drop into a power dive similar to that of a military pilot avoiding an adversary. In fact, to get the point across to his students, Yager sometimes shows them a clip from the movie Top Gun.

Mantids detect attacking bats by picking up their high-frequency or ultrasonic chirps, which at one time would have seemed like an impossible skill for a creature long believed to be deaf. But while a graduate student in the late 1980s, Yager discovered that most praying mantis species have single, or Cyclopean, ears deep in the center of their thoraxes. They enable the creatures to pick up sounds that are beyond the hearing range of humans. “The ear doesn’t look like any other ear,” says Yager, who is studying the auditory systems of insects. “They’re the only animals known to have just one ear.”

Mantids derive their common name from a different part of their anatomy—their front legs, which they hold at an angle suggesting prayer. There are some 2,300 species worldwide, including about 20 that range in the United States. Most are so-called “sit and wait” predators that feed on moths, crickets and other insects. Some of the bigger species can even snag a small lizard or hummingbird. But when they fly, especially at night, the hunters become the hunted.

In a series of nighttime experiments in southwestern Ontario’s Pinery Provincial Park, Yager and his colleagues released several mantises into a well-lit parking lot from atop a 15-foot ladder. A number of wild bats were cruising nearby, looking for prey. Each time one of them zeroed in on a mantis, the insect would dive in a tight spiral, “like a corkscrew,” says Yager. “It’s not just a fall. They go faster as they go down.” Sometimes the bat could follow; other times, it had to pull up. When a bat stayed on a mantis’ tail, the insect would hit the ground as a last resort. Being small and agile, it survived the crash. Without their ability to hear the bats, none of the mantises would have had a chance.

“We’re trying to understand the role of hearing in animals’ lives, such as how they use sound to survive,” says Yager, who has developed some new photographic techniques to study his subjects. For years, scientists thought some insects evolved ultrasonic hearing to avoid bats. But Yager and his colleagues recently uncovered evidence that praying mantises first developed their ear about 120 million years ago, long before the first bats appeared on the scene. He speculates a different kind of insectivorous predator could have been chasing them during the Cretaceous Period, which means mantids may have been honing their Top Gun skills since the Age of the Dinosaurs.